This invention is concerned with a method of increasing the detonation velocity of detonating fuse having an explosive core and a covering surrounding the explosive core. Detonating fuse has many applications in explosive work and is an integral component of many types of downhole well perforating guns. Such detonating fuse consists of an explosive core, typically of cyclotrimethelen trinitramine (RDX), with a textile or plastic covering. Detonating fuse of this type is commercially available from Ensign-Brickford under the mark Primacord.
In a perforating gun, the detonating fuse is strung the length of the gun and is connected to the rear of each of the charges mounted on a bar, or charge carrier. Detonation of the detonating fuse is designed to detonate each of the charges simultaneously by transferring an explosive detonation wave through the detonating fuse. When the charges don't fire simultaneously, those which detonate first hinder the effectiveness of those charges which detonate later, and in some cases prevent altogether the detonation of subsequent charges. Lack of substantially simultaneous charge detonation drastically reduces the extent and efficiency of perforating the stratum.
Lack of substantially simultaneous charge firing commonly results from failure of the detonating fuse, upon detonation, to furnish a shock wave of sufficient velocity to initiate the firing of each of the charges. Sometimes the detonating fuse as manufactured, simply lacks sufficient detonating velocity. In other situations, however, the direct exposure of the detonating fuse, when used in the bar gun application, to the elevated temperature and pressure found in the borehole of a well can significantly lower the effective velocity attained by such detonating fuse upon detonation. The elevated downhole temperature and pressure cause shrinkage of the covering of the detonating fuse, and the resulting pinching, kinks and crimps therein reduce effective detonation velocity.
A method of increasing the detonation velocity of detonating fuse is therefore especially useful in downhole applications to be able to consistently achieve simultaneous detonation of all charges in a perforating gun.